The inorganic perhydrate bleach most widely used in laundry detergent compositions is sodium perborate in the form of either the monohydrate or tetrahydrate. However, an increased interest in other perhydrate salts is being observed, of which sodium percarbonate is the most readily available.
Detergent compositions containing sodium percarbonate are known in the art. Sodium percarbonate is an attractive perhydrate for use in detergent compositions because it dissolves readily in water, is weight efficient and, after giving up its available oxygen, provides a useful source of carbonate ions for detergency purposes.
The inclusion of percarbonate salts in laundry detergent compositions has been restricted hitherto by the relative instability of the bleach. In particular, percarbonate salts decompose rapidly when stored in a moist and/or warm atmosphere. It is known that acceptable storage characteristics may however be obtained through the protection of the carbonate by coating the crystalline product, or by the inclusion of stabilizing agents during its manufacture, or both. A variety of suitable coating agents have been proposed including silicates and mixtures of inorganic sulphate and carbonate salts.
In WO92/06163 are described percarbonate-containing compositions wherein the Equilibrium Relative Humidity as well as the level of heavy metal ion have to be carefully controlled to ensure percarbonate stability.
There is still, however, the need to improve storage stability of the percarbonate bleach, and to achieve this in all types of detergent compositions, including compositions made by the various making processes currently available.
The Applicants have however unexpectedly discovered that when a hydrophobic material selected from silica, talcs or waxes is used into the detergent compositions, in certain ratios to percarbonate particles of a determined size, and particularly when said hydrophobic material such as silica is used as dusting agent onto said percarbonate particles prior to their incorporation into the composition, the storage stability of the percarbonate is remarkably improved, in all types of compositions, including dishwashing compositions adapted for use in automatic dishwashing.
The use of silica as flow aid for detergent granules is known in the art, although the art usually does not distinguish between the different types of silica most advantageous for this purpose; in many cases, the use of precipitated silicas which are mainly hydrophilic, are described.
JP 61 069897, laid open Apr. 10, 1986 states that aluminosilcate, silicon dioxide, bentonite and clay having an average particle diameter of not more than 10 micrometers can be used as a surface modifier at a level of from 0.5% to 35%; Percarbonate is merely mentioned among the bleach ingredients.